He started by saying that the game was originally developed in just "five very long days," and was created for the Experimental Gameplay Project and based around simplicity -- it only uses six colors and, obviously, the one button. For a game that's so simple, it actually had a lot of complex influences. It drew from older games, like Another World and Flashback, as well as modern works, like Half-Life 2 and District 9.
The level design was originally assembled around the idea that "the farther you go, the harder it gets," but they later evolved the difficulty to be based around the player's running speed, so that, to an extent, you could self-mediate the difficulty by hitting obstacles and slowing down a bit. The buildings were all designed with what Johnson called "lego pieces" -- little bits of graphics that are interchangeable to create somewhat randomized designs.
Jackson said no matter what the reasons, having a free Flash version to play worked great for them (they shared that they'd sold 115,000 copies on the App Store in just five months), and while the server costs of keeping a popular game up online are not insignificant, Semi Secret Software will continue to do the same thing with their future games (in fact, you can currently play Gravity Hook HD, their next game, online right now even before it's released on the iPhone.
The other decision they made on marketing was with price -- despite calls to the contrary, they decided to stick with the $2.99 price on the iPhone. That proved to be very "polarizing" -- almost all of their App Store reviews mentioned the price, both positively ("this is totally worth the money") or negatively ("How dare you charge this much"). They believed that while they would have sold more copies at 99 cents, the $2.99 price gave them a different type of customer, and as they showed with the chart below, they got a different type of reviewer. Free apps, they said, tend to attract a lot more negative reviews in general, while people who pay for paid apps tend to take a little more "ownership" in the game they support.
We'll keep an eye out for both Gravity Hook HD and Flixel, and we'll try to corner the guys from Semi Secret later this week to try and talk to them both about their work on Canabalt and what they're up to in the future.